fix wrong canvas caching
fixes #59 WebGLRenderer not cleaning up old stage

Add cleanup logic to WebGLRender to so if the stage is changed, sprites from the previous stage are not left behind.
Merge pull request #60 from RobertWHurst/master

WebGLRender should cleanup previous stage.
fix for rendering different stages
merge file issue
Merge pull request #49 from ze0nni/master

Texture Cache